The present invention pertains to ceramic items and methods for preparing ceramic items and more particularly pertains to ceramic articles, tools, and methods for preparing ceramic articles and for sintering.
Zirconia (ZrO.sub.2) is a ceramic material, which, in its tetragonal crystal structure, is strong and tough and can be made into tools and other articles, but has the shortcoming that it is relatively soft. Repeated wear and abrasion of the surfaces of a tetragonal zirconia part or tool, however, can cause a phase transformation of the surface from tetragonal phase to monoclinic phase, which is harder than tetragonal phase. The result is a tool which has a hard "case", that is, one or more hard outer surfaces, and a tough inner portion or "core", but the wear or abrasion may be uneven which presents another shortcoming. Zirconia also exists in a cubic crystallographic structure, which is even harder than monoclinic phase, but more brittle. Cubic phase zirconia requires high temperatures for its formation; however, an alloy of zirconia and an oxide of yttrium, magnesium, scandium, cerium or calcium can provide a stable cubic phase at room temperature.